Expert comment: Storm Isha

“After a period of very cold and settled weather, the weather regime is forecast to change to become stormy again with weather warnings already issued for storm Isha, which was named today (19th January) and is approaching the UK on Sunday. 

“The Met Office has issued amber and yellow severe weather warnings over large regions of the UK for strong winds and heavy rain on Sunday and Monday. As usual, the details of these warnings may change as Isha approaches and the forecasts become more certain. 

“Storm Isha is the 9th named storm of the season, which runs from September to August each year. 

“The Met Office began naming storms in 2015 to improve public awareness of these storms with the aim of reducing the harm they can cause. The storms are named in collaboration with the Irish and Dutch meteorological services for storms impacting western Europe. However, if a storm has already been named by another country, or was previously named as a hurricane, then it keeps that name. 

“The number of storms named varies each year with only two storms named by the Met Office in 2022-23: Antoni and Betty, both in August. However, two other storms, named by other meteorological services, also impacted us earlier that year (Otto and Noa). 

“Only once previously has a storm been named by the Met Office by a name beginning with “I”. That was storm Imogen, which hit the UK/Ireland on 8 February 2016. 

“The UK often experiences strong hazardous storms like Isha, particularly in the autumn and winter. These storms normally develop over the North Atlantic and we are positioned at the end of the typical track of these storms. The “jet stream”, the ribbon of strong winds travelling towards the east at about 10 km height in our atmosphere, is important for the development of these storms and helps direct them towards us. 

“The number of storms that impact us each year can be influenced meteorological phenomena occurring elsewhere across the globe such as the current El Niño event in the tropical Pacific region.  El Niño is a naturally occurring event occurring every few years that is associated with sea surface temperatures in the central-east equatorial Pacific being warmer than average. 

“It is difficult to predict how extratropical cyclones are being and will be affected by climate change because there are several different influences on them that are likely to be affected by climate change. There is some evidence though that storms with strong winds (windstorms) will become slightly more frequent in the future in northwest Europe and also become more “clustered”, so that we experience several storms one after the other. There is strong evidence that on average storms will produce more rainfall and some studies have also predicted an increase in the strength of the winds in the strongest storms.”